Theoretical FRET Efficiency of an Antenna Material Containing Natural Dyes and Zeolite L.

We calculated the Förster resonance energy-transfer (FRET) efficiency of a theoretical host-guest composite formed by all-trans ß-cryptoxanthin (BCRY), all-trans zeaxanthin (ZEA), and a zeolite-LTL (Linde Type L) nanochannel with the help of computational chemistry tools. Climate change demands urgently the development of novel renewable energies, and in such a context, artificial photosynthesis arises as a promising technology capable of contributing to satisfying humankind's energy needs. All artificial photosynthetic devices need antennas to harvest and transfer energy to a reaction center efficiently. Antenna materials integrated by highly fluorescent synthetic pigments embedded onto the nanochannels of a zeolite-LTL have already been shown experimentally to be very efficient supramolecular assemblies. However, research work computing the efficiency of an antenna made of nonfluorescent natural pigments and a zeolite-LTL nanochannel has not been undertaken yet, at least to our knowledge. Fortunately, natural dyes possess outstanding features to study them dynamically; they are environmentally friendly, inexpensive, ubiquitous, and abundant. Density functional theory (DFT) methods were chiefly employed along with the CAM-B3LYP functional and the 3-21G*/6-311+G(d,p) basis sets. The ONIOM method enabled geometry and energy calculations of dyes inside the zeolite-LTL (ZL) nanochannel. The Förster resonance energy-transfer (FRET) efficiency and the Förster radius of the composite were 40.9% and 24.9 Å, respectively. Theoretical findings suggested that this composite might contribute to diminishing costs and improving the environmental friendliness of an antenna system.

Geometric description and electronic properties of the principal photosynthetic pigments of higher plants: a DFT study.

The geometric parameters, local and global chemical reactivity parameters (such as the ionization potential, electron affinity, electronegativity, hardness, softness, chemical potential, and electrophilicity index), as well as the energy levels (HOMO/LUMO) and HOMO-LUMO energy gaps have been determined for the principal carotenoids in higher plants. DFT calculations performed using the B3LYP functional in combination with the 6-31G(d,p) (for geometric parameters) and 6-31 + G(d,p) (for energy parameters) basis sets were carried out to study these structures. The HOMO-LUMO energy gaps obtained with the TPSSh functional were compared with the corresponding energy gaps obtained with B3LYP (when both functionals were used with the 6-31 + G(d,p) basis set). Upon analyzing all of the calculated parameters of the studied molecules, both carotenes were found to be the most reactive, followed by ß-cryptoxanthin, zeaxanthin, lutein, violaxanthin, and finally neoxanthin, the least reactive molecule. The results reveal that all of the carotenoids show very high coplanarity in the photochemically active region, resulting in small HOMO-LUMO energy gaps. The calculated local and global chemical reactivity parameters indicate that all of the studied molecules may be classified as soft, as they are good electron donors/acceptors, making these molecules good candidates for use in artificial photosynthetic systems.

Platinum electrodeposition on unsupported carbon nano-onions.

An effort to develop smaller, well-dispersed catalytic materials electrochemically on high-surface-area carbon supports is required for improved fuel cell performance. A high-surface-area carbon material of interest is carbon nano-onions (CNOs), also known as multilayer fullerenes. The most convenient synthesis method for CNOs is annealing nanodiamond particles, thus retaining the size of the precursors and providing the possibility to prepare very small nanocatalysts using electrochemical techniques. In terms of pure metal catalysts, platinum is the most common catalyst used in fuel cells. The combination of Pt nanoparticles with CNOs could lead to new catalytic nanomaterials. In this work, this was accomplished by using a rotating disk-slurry electrode (RoDSE) technique. The Pt/CNO catalysts were prepared from slurries that contained functionalized CNOs and K(2)PtCl(6) as the platinum precursor in aqueous 0.1 M H(2)SO(4) solution. X-ray photoelectron spectroscopy results showed that 37% of the Pt on the CNOs is metallic Pt whereas 63% had higher binding energies, which is evidence of higher oxidation states or the presence of Pt atoms and clusters on CNOs. However, aberration-corrected scanning transmission electron microscopy of the Pt/CNOs confirmed the presence of Pt atoms and clusters on CNOs. Thermal gravimetric analysis showed the excellent thermal stability of the Pt/CNOs and a lower onset potential for the electrochemical oxidation of methanol compared to that of commercial Pt/Vulcan catalyst material. The computational method confirmed the Pt atoms' location at CNOs surface sites. Geometric parameters for distances between Pt atoms in the 3Pt/CNOs molecular system from our theoretical calculations are in agreement with the respective parameters obtained experimentally. The combination of CNO with RoDSE presents a new highly dispersed catalyst nanomaterial.

Computational study of Au_4 cluster on a carbon nanotube with and without defects using QM/MM methodology.

We use ONIOM (QM/MM) methodology to carry out geometry calculations in a 4-atom nanocluster supported by an (8, 8) armchair carbon nanotube with and without defects employing LSDA/SDD for the QM system and UFF for MM. In two particular cases, defects were added in the carbon nanotube wall. These defects are a double oxygenated vacancy (Vac2O2) and a double vacancy but without oxygen which creates two pentagons and an octagon. Our results show how geometries using QM/MM and energies calculations carried out with QM, change on both the gold nanocluster and the carbon nanotube. In addition, an application of ONIOM methodology in a comparative study to predict behavior of structures as hybrid materials based in carbon nanotubes combined with gold nanoclusters is shown. In this work we examine geometry changes on both the gold nanocluster and the carbon nanotube. A comparison is made with the binding energy resulting values as well as with the orbital energies such as the frontier orbitals HOMO and LUMO.

Computational characterization of sodium selenite using density functional theory.

In this theoretical study we used density functional theory to calculate the molecular and crystalline structures of sodium selenite. Our structural results were compared with experimental data. From the molecular structure we determined the ionization potential, electronic affinity, and global reactivity parameters like electronegativity, hardness, softness and global electrophilic index. A significant difference in the IP and EA values was observed, and this difference was dependent on the calculation method used (employing either vertical or adiabatic energies). Thus, values obtained for the electrophilic index (2.186 eV from vertical energies and 2.188 eV from adiabatic energies) were not significantly different. Selectivity was calculated using the Fukui functions. Since the Mulliken charge study predicted a negative value, it is recommended that AIM should be used in selectivity characterization. It was evident from the selectivity index that sodium atoms are the most sensitive sites to nucleophilic attack. The results obtained in this work provide data that will aid the characterization of compounds used in crop biofortification.